Hydrogen Peroxide Generation and Hydrogen Oxidation Reaction Properties of Ir(111)-, (100)-, and (110)-Low-Index Single-Crystal Surfaces

Hydrogen peroxide (H2O2) generation and hydrogen oxidation reaction (HOR) properties of Ir(hkl) (hkl = 111, 100, and 110) were investigated in acidic media using scanning electrochemical microscopy. In the 0.06-0.3 V vs reversible hydrogen electrode potential region, H2O2 generation properties were significantly suppressed for the Ir(hkl) surfaces in comparison with Pt(111): only the Ir(100) revealed slight evolution of H2O2 at ca. 0.1 V. Conversely, the HOR activity trend of the Ir(hkl) was Ir(111) > Ir(100) > Ir(110), and the activity of Ir(111) is approximately 70% of that of Pt(111). This study presents Ir-based nanosized catalysts whose surface comprises mainly (111) facets (such as octahedron-shape) as effective anode catalysts for polymer electrolyte fuel cells.